fix(reusable-trivy): sparse-checkout .trivyignore for the image scan gate

.github/workflows/reusable-trivy.yml

@@ -158,6 +158,22 @@ jobs:
       actions: read
       packages: read
     steps:
+      # Trivy's --ignorefile flag defaults to ".trivyignore" in the working
+      # directory for every scan type, image included. Without a checkout
+      # here, the job's cwd never has the caller repo's .trivyignore, so a
+      # repo has no way to document an accepted, unfixable base-image CVE
+      # (e.g. a Debian `<no-dsa>` glibc issue) without the gate blocking
+      # every future push indefinitely. Sparse-checkout only that one file —
+      # a full checkout would also auto-load a root-level trivy.yaml (per the
+      # iac-license job's own config comment above), silently coupling that
+      # fs/license-scan config to this unrelated image gate.
+      - name: Sparse checkout .trivyignore
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          sparse-checkout: |
+            .trivyignore
+          sparse-checkout-cone-mode: false
+
       # image-ref is a ghcr.io reference by digest (see the usage comment at
       # the top of this file). `permissions: packages: read` alone does not
       # authenticate the docker/trivy pull for a private package - confirmed